Colour prediction of organic dye molecules on a microcomputer—a readily available form of the PPP-MO method for teaching and research

The Pariser-Parr-Pople molecular orbital (PPP-MO) method, which provides a way of calculating electronic absorption spectroscopic properties of organic dye molecules, such as the position of the absorption maximum in the visible spectrum, its intensity and polarisation direction, has been implemented in PASCAL language on a 64 kB Apple 11 computer. The system consists of two modes: (1) Graphic mode and (2) PPP mode, which are controlled separately or successively. The system occupies up to 32 kB of memory, needs 1 minifloppy disk in the entire execution of the program, and handles up to 30 atoms routinely with configuration interaction.     

Purification and properties of three albumins from Triticum aestivum seeds

Three albumins were isolated from bread wheat seeds by gel filtration on Sephadex G-100 and differential preparative disc-electrophoresis on polyacrylamide gel. The proteins were obtained in sufficient yield and purity to carry out characterisation studies. The electrophoretic mobilities of the three albumins in polyacrylamide discs in glycine—Tris medium, pH 9·5, were 0·28, 0·34 and 0·39 (referred to that of bromophenol blue taken as 1). The isoelectric points were 6·40, 6·40 and 5·35 and the molecular weights 17, 700, 18, 200 and 18, 900, respectively. The amino acid compositions of the purified albumins were very similar. The correlation of the purified albumins with those isolated from bread wheats by other authors is discussed.     

Smoke dilution methods for the evaluation of the smoke emission from burning polymers: A comparative approach

A comparative approach to the determination of smoke emission from burning polymers has been attempted, and a number of combustion conditions and detection devices have been tried to choose a test method for measuring the smoke proiduction of materials. The combustion apparatus adopted is a hot-air quartz furnace that permits the measured by dynamic method from combustion of PAN, PVC and PVC mixed with some metal oxiders, have been compared with those obtained by an accumulation mode. For PVC the intensity of the light scattered from the evolving smoke has been measured as an alternative to smoke density.     

An application of pruning in the design of neural networks for real time flood forecasting

We propose the application of pruning in the design of neural networks for hydrological prediction. The basic idea of pruning algorithms, which have not been used in water resources problems yet, is to start from a network which is larger than necessary, and then remove the parameters that are less influential one at a time, designing a much more parameter-parsimonious model. We compare pruned and complete predictors on two quite different Italian catchments. Remarkably, pruned models may provide better generalization than fully connected ones, thus improving the quality of the forecast. Besides the performance issues, pruning is useful to provide evidence of inputs relevance, removing measuring stations identified as redundant (30–40% in our case studies) from the input set. This is a desirable property in the system exercise since data may not be available in extreme situations such as floods; the smaller the set of measuring stations the model depends on, the lower the probability of system downtimes due to missing data. Furthermore, the Authority in charge of the forecast system may decide for real-time operations just to link the gauges of the pruned predictor, thus saving costs considerably, a critical issue in developing countries.

A kinetic study of the metathesis of propene on a rhenium-aluminium catalyst

Based on integral kinetic measurements and in accordance with the results of previous investigations, two mechanistic initial rate expressions based on different reaction mechanisms have been found to be statistically equivalent. Applying the Boudart criteria in a test for the physical significance of the parameter estimates, only one of the suggested expressions is significant and the corresponding reaction mechanism is, therefore, considered adequate.     

Current-switching half adder

A new current-switching half adder is described; rise and fall times of about 3 ns have been obtained.